In recent years, a recording medium including a coating layer used as offset printing paper has been employed in an image forming method by water-based inkjet. However, unlike a recording medium without a coating layer, inks hardly penetrate the recording medium including a coating layer. Thus, coalescence of droplets occurs on paper, and there is a problem of bleeding between inks of different colors or between the inks and the recording medium.
In order to solve the problem, in a case where a water-based ink is discharged on a recording medium including a coating layer, there is proposed a method for preventing bleeding by promoting agglomeration of a pigment in the water-based ink.
Specifically, in the method, a recording medium designated for water-based inkjet image formation is prepared and used by treating a recording medium including a coating layer so as to impart pigment agglomeration promoting function. However, this method has a problem of that the recording medium is limited.
Meanwhile, for a recording medium without a coating layer such as plain paper, a method of applying a pre-treatment liquid which agglomerates a pigment in an ink immediately before ink discharge is proposed.
For example, there is proposed an inkjet recording method to apply on plain paper a reaction liquid including polyallylamine and an ink composition including a colorant and a resin emulsion for printing (see PTL 1).
Also, there is proposed an inkjet recording method to apply on plain paper a reaction liquid including an ammonium salt of an organic acid and a water-soluble cationic polymer and an ink composition including a colorant and a resin emulsion for printing (see PTL 2). These proposals are directed to plain paper including no coating layer as the recording medium. When the recording methods by these proposals are applied to a case where a recording medium including a coating layer is used and a large quantity of a pre-treatment liquid is used, e.g. high-speed continuous printer, there are risks of occurrence of a failure in a conveying member of the apparatus and degradation of image quality due to accumulation of contamination. That is, when the treatment liquid is applied, the pre-treatment liquid contacts with the conveying member before an inkjet discharge step, causing the pre-treatment liquid transferred to the conveying member. Thus, there arise problems of occurrence of a failure in the conveying member and degradation of image quality due to accumulation of contamination.
In order to solve the problem, an image forming method including a drying step for drying a treatment liquid has been studied, where the treatment liquid is dried quickly after it is applied. The image forming method including the drying step can solve the problem of the pre-treatment liquid transferred to the conveying member. However, an agglomeration function of the treatment liquid degrades through the drying step. As a result, there arises a new problem of degraded image quality due to degraded function of bleeding prevention.